In the past, in order to lay down underground pipelines, trenches were dug and the pipes were placed in the bottom of the trenches. After the pipes had been leveled, the trenches were generally re-filled with the ground that had been previously dug up.
However, more recently, directional drilling has been used to drill holes underground to assist in the laying down of pipelines and other utilities so that less work is required to re-fill trenches.
In directional drilling, a large hole is initially dug out to align with the depth that the pipe is to be installed so that the directional drilling apparatus may be assembled. Prior to operation, a motor is connected to a mandrel which is used to create a guide line along which the pipe is to be laid down. The motor causes the mandrel to rotate creating a small hole. The directional drilling apparatus may further comprise means for aligning the mandrel and for constantly watching the digging of the guide line. The drilling of the guide line results in a small hole being created from the location of the motor to the large hole. After the mandrel reaches the large hole, a reamer is connected to the mandrel along with the pipe that is to be laid down. The motor is once again enabled to rotate the mandrel and to draw the mandrel, reamer and pipe. This requires a number of increasingly larger passes at which time the reamer and pipe are pulled towards the motor. The rotation of the motor causes the size of the guide line hole to increase allowing the pipe to be laid down.
During the hole producing process, liquid, in the form of bentonite or other drilling fluid is released via jets in the drilling apparatus. The bentonite mixes with the ground to create a slurry which is passed backwards against the surface of the pipe to the large hole. In order to provide space for the slurry to travel, the circumference of the reamer is generally one and half times larger than the circumference of the pipe. This extra space allows the slurry to travel towards the hole but also allows for frac-outs to occur. A frac-out is the uncontrolled spilling of drilling fluids, usually bentonite, into the environment. This happens when the hole being drilled fractures or collapses and the fluids that are used to lubricate the drill seep out of the hole. Frac-outs can be devastating to the environment.